Paint Coverage Calculator
Calculate exactly how many gallons or liters of paint you need.
Enter wall area, coverage rate, and number of coats for accurate estimates.
Paint Needed
Paint coverage calculation ensures you buy the right number of gallons before starting a project — avoiding costly return trips mid-paint or expensive leftover waste.
Basic formula:
Paintable Area (sq ft) = (Perimeter × Wall Height) − Doors − Windows
Gallons Needed = Paintable Area / Coverage Rate × Number of Coats
Standard coverage rates:
| Paint Type | Coverage per Gallon |
|---|---|
| Flat / matte | 350–400 sq ft |
| Eggshell / satin | 350–400 sq ft |
| Semi-gloss / gloss | 300–350 sq ft |
| Primer (first coat) | 200–300 sq ft (porous surfaces) |
| Exterior paint | 250–400 sq ft |
Worked example — 12 × 14 ft bedroom with 9-ft ceilings:
- Perimeter: 2 × (12 + 14) = 52 ft
- Wall area: 52 × 9 = 468 sq ft
- Subtract door (21 sq ft) + window × 2 (24 sq ft): 468 − 45 = 423 sq ft paintable
- Two coats at 350 sq ft/gal: (423 / 350) × 2 = 2.42 gallons → buy 3 gallons
Deductions reference:
- Standard door (30" × 80"): ~17 sq ft per side; skip if painting the door
- Standard window: 12–15 sq ft per window
Always buy 10–15% extra for:
- Touch-ups in months or years ahead
- Roller and brush absorption (rollers absorb 0.25–0.5 oz/sq ft)
- Trim loss at edges and corners
Color change rule: Painting over a dark color with a light one (or vice versa) almost always requires a primer coat + 2 finish coats — plan for 3 total applications.